KUALA LUMPUR — Irene Fernandez has no shortage of shocking tales of the abuse and exploitation of foreign domestic workers in Malaysian homes.

One Cambodian woman, who said she was forced to cook, clean and care for children from 5 a.m. until past midnight, told Ms. Fernandez that her employer once tied her hands behind her back and ordered her to leap down a flight of stairs, leaving her with a permanent limp.

Another domestic helper, also from Cambodia, reported that she used to suck the fish bones left on her employer’s dinner plate, because she was only given leftovers to eat.

“It’s so dehumanizing,” Ms. Fernandez said. “To me, it’s just slavery days coming back — and that’s just frightening.”

Such cases have come to dominate the life of Ms. Fernandez, whose grandmotherly appearance masks seemingly bottomless reserves of energy to speak up for the millions of foreign workers who toil in Malaysian homes, palm oil plantations, construction sites and other jobs often shunned by Malaysians.

A leading figure in civil society and a longtime member of the political opposition, Ms. Fernandez’s habit of not mincing her words has often landed her in trouble with the authorities.

She gained international attention as the face of one of the country’s longest-running criminal trials after she was charged in 1996 with publishing falsehoods in a report on the abuse of migrants in government detention centers. More recently, she has come under investigation over possible sedition after she declared that Malaysia was not safe for foreign workers.

Now 66 and with osteoarthritis often forcing her to use a wheelchair, Ms. Fernandez appears to have lost little of the vigor that has driven her to seek justice for migrant workers, insisting that she will continue providing a voice for the vulnerable as long as she is able.

The executive director of Tenaganita , a nongovernmental group she established more than two decades ago to help foreign workers, Ms. Fernandez’s connection to migrants can be traced back to her familial roots. Her parents were Indians who came to Malaysia to work on a rubber plantation when the country was under British rule.

Ms. Fernandez learned early on that not everyone was treated equally, recalling how, as the daughter of a supervisor, she was not supposed to play with the laborers’ children.

“I always found that a big conflict in me,” she said.

Ms. Fernandez’s first job was as a teacher, but at the age of 23, she left the security of a government job for the uncertain life of an activist. Stints at various labor and rights groups followed, including the Young Christian Workers Movement and later the women’s rights movement.

“After two to three years I felt that the whole advocacy was taken over by middle-class women and there was a gap for me where women workers were concerned, and that’s how, in 1991, I formed Tenaganita,” she said in an interview at the organization’s office in a Kuala Lumpur suburb.

Tenaganita — “women’s force” in Malay — runs shelters for migrants and victims of human trafficking who have been abused or exploited and helps them seek legal recourse. It initially focused on women but has expanded to include male migrants.

Rights groups estimate that Malaysia is home to about four million foreign workers, about half of whom are undocumented, making them particularly vulnerable to abuse. Most are from Indonesia, the Philippines, Nepal, India and Bangladesh.

The accounts of abuse she has heard led Ms. Fernandez to conclude that Malaysia does not do enough to protect migrant workers, she told The Jakarta Post, an Indonesian newspaper, in May.

Her allegations were not new. It was only last year that Indonesia lifted a ban on women going to Malaysia as domestic workers that had been imposed in 2009 after a string of abuse cases. But Ms. Fernandez’s comments prompted a police investigation into whether she had contravened the country’s Sedition Act.

“While there may not be specific laws for migrant workers, Malaysia has sufficient laws to protect all workers, including foreign workers,” Ms. Maznah was quoted as saying in The Star, a Malaysian newspaper.

A police spokesman said Monday that the investigation was still under way and it had not yet been decided whether to charge Ms. Fernandez. Charges may be less likely given that Prime Minister Najib Razak recently announced that he intends to repeal the Sedition Act.

Ms. Fernandez, who is married to the former chairman of Amnesty International’s Malaysia chapter and has three children, two of whom work with her, has refused to back down from her comments, displaying a tenacity evident during an earlier, 13-year legal battle.

She was arrested in 1995 and charged the following year with “maliciously publishing false news” over her report on the treatment of migrants in detention centers. Convicted in 2003 and sentenced to one year in jail, she was released on bail while her appeal was heard. She was not acquitted until 2008, by which time she had spent almost 1.5 million ringgit, or about $475,600, fighting the charges.

“It was a classic case of a government more interested in harassing a human rights defender than taking concrete action to address the issues that she was raising,” said Phil Robertson, deputy Asia director at Human Rights Watch.

Mr. Robertson described Ms. Fernandez as “the pioneer of protection for migrant workers who everyone else has followed.”

“She’s brave and committed, and ready to battle daily for what she believes is right,” he said in an e-mail. “She was one of the first persons who recognized the dire human rights situation migrant workers face in Malaysia.”

Kamal Malhotra, the U.N. resident coordinator for Malaysia, said the United Nations is monitoring the current police investigation and that the official reaction to Ms. Fernandez’s comments had been “unfortunate and somewhat excessive.”

“We hope the case will not be prolonged this time and that the outcome will be different from the 2003 one,” he said in an e-mail.

Mr. Malhotra noted that Tenaganita, which has worked with various U.N. organizations, has also worked with government agencies to help address issues like trafficking. “So their role has not only been one of critic of the government but also constructive advocate,” he said. “This is too often forgotten.”

Ms. Fernandez’s activism led her to politics. She is a founding member of the opposition People’s Justice Party, serving on the party’s leadership committee for 12 years.

Because she had been convicted of a crime, she was barred from running for office in the 2004 and 2008 elections. While her acquittal means that she could run in the next election, which must be held by April 2013, Ms. Fernandez said she had decided not to run.

“My health is not too good, and you need a lot of energy to manage your constituency,” she said. “You also need a certain amount of finances and, being a human rights activist, your finances are always low.”

Ms. Fernandez rejects any suggestion that being aligned with the opposition leaves her vulnerable to claims of bias against the government in her work as an activist.

“The criticism comes from our work with the people,” she said. “The government must recognize that. We speak from evidence. We speak from the experiences lived by the people, by women, by migrants, by refugees.”

Her political ambitions may not have been realized, but she has no plans to pull back from her work with Tenaganita. There, she continues to encounter the stories that inspire her to keep fighting, like a 15-year-old girl from Uzbekistan who was forced into prostitution after arriving in Malaysia.

“Before she left, she said, ‘Thank you for giving me life again,”‘ Ms. Fernandez said. “That was so wonderful for me — that we could help people to have the hope of life again.”